Liquid alkali for reactive dyeing of textiles

ABSTRACT

A liquid alkali composition for use in fiber reactive dyeing of cotton and cotton blended fabrics or the like. The liquid alkali is a solution of sodium hydroxide, potassium hydroxide, and potassium carbonate formed by reaction of CO 2  with the potassium hydroxide solution, and adding sodium hydroxide to the resultant mixture. The resulting supersaturated solution has a high enough Total Alkalinity to achieve reaction between the dye, including vinyl sulfone dyes, and fiber but is sufficiently buffered to achieve this reaction slowly so that the fiber reactive dyes fix in a level, uniform fashion. Preferably the composition includes potassium carbonate, potassium citrate, and potassium polyacrylate. The citrate and polyacrylate act as dispersants in the dyeing process and also act as crystallization inhibitors in solution. The use of the carbonate compounds of the present invention in place of conventional silicates or phosphorus prevents the discharge of untreatable toxic wastewater into natural waterways.

This is a division of application No. 08/466,353, filed Jun. 6, 1995,now U.S. Pat. No. 5,603,736 issued Oct. 9, 1998, which is acontinuation-in-part of application No. 08/327,041, filed Oct. 21, 1994,now abandoned, which is a division of application No. 07/874,754, filedApr. 27, 1992, now U.S. Pat. No. 5,382,262.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates generally to buffered alkalis for use inthe dyeing of textiles, as well as for use in paper processing, wastetreatment and laundry and dishwashing uses and, more particularly, to aliquid alkali for use in fiber reactive dyeing of cotton and cottonblended fabrics.

(2) Description of the Prior Art

Fiber reactive dyes were first introduced in 1956. Since that time theyhave become a dominant factor in dyeing cotton, regenerated celluloseand blends. These dyes can also be used to dye acrylics, nylon, silk,and wool and blends of these fibers. Fiber reactive dyes are easy toapply and produce brilliant shades, fastness, penetration and leveling.

Fiber reactive dyes are anionic in nature and react chemically with thefiber. The dyes include a chromophore to give color to the dye and areactive group to form a chemical bond with the fiber. There may also bea substituent or solubilizing group which provides additional dyeingcharacteristics such as solubility, substantivity, migration, washingoff, etc. Fiber reactive dyes react in the presence of alkali to form astrong covalent chemical bond between a carbon atom of the dye moleculeand an oxygen atom of the hydroxyl group in the cellulose. This step iscalled “fixing”.

The following alkalis have all been used to obtain the “fix” ofdifferent classes of reactive dyes to cellulose fibers:

Sodium Hydroxide Potassium Hydroxide Trisodium Phosphate SodiumTripolyphosphate Sodium Carbonate Sodium Bicarbonate Sodium Silicate

However, no single alkali system has worked on all classes of reactivedyes due to the differences in the rate of hydrolysis of each dye. Ofall the alkali systems, the liquid phosphate system described in U.S.Pat. No. 4,555,348, issued to Moran, and sold under the tradenameAlkaflo by Sybron Chemicals of Birmingham, N.J., works almostuniversally. But Alkaflo is high in phosphorus which can contribute toenvironmental problems.

Another commercial liquid alkali is sold under the tradename Burco NP-QSalt and is available from Burlington Chemical Co., Burlington, N.C.This product is based on a mixture of sodium hydroxide, potassiumhydroxide, soda ash, citrate, acrylate salt. The resultingneutralization/buffer curve is similar to the phosphorus-based Alkaflo.The problem with both NP-Q Salt and Alkaflo is that hydrolysis is stilltoo quick when using Trichlor Pyrimidine, Difluorchlor Pyrimidine orDichlorchinoxaline dyes (sold under the tradename “Levafix” andavailable from ICI America, Wilmington, Del.). While these alkalis aresuitable for sulfatoethysulfone or chlortriazine dyes, they are too“hot” for the Levafix-type colorants.

Another alkali which has been used on and off, as discussed above, issodium carbonate. In difficult dyeing situations, i.e., matching shadeswith reactive dyes of differing reactivities, sodium carbonatedemonstrates the best overall dyeing performance because of high TotalAlkalinity and good buffering. The problem with sodium carbonate is thatit takes 20% on weight of bath (OWB) to fix the dye. Unfortunately, themaximum g/L total solubility of sodium carbonate (approximately 25%)limits the concentration of the liquid alkali that can be produced. Inaddition, using the alkali as a powder is not feasible in modern dyeingequipment.

The problem with using a solution of sodium carbonate is furthercomplicated due to changes in dyeing that occur when adding largeamounts of liquid to dyebaths, i.e. changes in liquor ratio or fabric towater ratio. In essence, when large volumes of liquid are added toreactive dyebaths, a dilution occurs which changes the concentration ofthe dye in contact with the fiber. Therefore, it is advantageous to addas low a volume of alkali as possible.

Assuming a sufficiently concentrated solution could be prepared, thebest product would be a liquid alkali with a high enough TotalAlkalinity to achieve the reaction between the dye and fiber butsufficiently buffered to achieve this reaction slowly so that the dyefixes in a level uniform fashion. The difference between the Active andTotal Alkalinities is especially important, the greater thedifferential, the better the ultimate performance.

However, if the reaction mixture is too “hot” or alkaline, such as isseen with pure sodium hydroxide, the sensitive-type reactive dyes willhydrolyze with the water in the dyebath and form a nonreactive pigmentthat has no effect on the fabric color. Furthermore, as fashions havechanged, the need to mix reactive dyes of different chemistries in thesame shade and the necessity of developing a universal alkali system forcold pad batch dyeing that does not contain silicates or phosphorus hasbecome more important.

On the other hand, the reaction mixture must be have sufficient activecaustic alkalinity to meet the reaction requirements of the dyes beingused, vinyl sulfone dyes, in particular, will require a hotter or morealkaline environment.

Thus, there remains a need for a liquid, phosphorus and silicate-free,alkali for use in fiber reactive dyeing of cotton and cotton blendedfabrics which has a buffer curve similar to sodium carbonate but withthe clean dyeing properties of a phosphorus-based system such asAlkaflo, and an active alkalinity sufficient to meet the dyeingrequirements of the particular dye being used.

SUMMARY OF THE INVENTION

The present invention is directed to a liquid alkali useful for avariety of applications, especially for use in dyeing of cotton andcotton blended fabrics. The liquid alkali is a solution of an alkalimetal hydroxide and its carbonate formed by reaction of liquid CO₂ withthe alkali metal hydroxide solution. The resulting supersaturatedsolution has a high enough Total Alkalinity to achieve reaction betweenthe dye and fiber but is sufficiently buffered to achieve this reactionslowly so that the fiber reactive dyes fix in a level, uniform fashion.Preferably the composition is a mixture of potassium hydroxide,potassium carbonate, sodium citrate, and polyacrylic acid. The citrateand polyacrylate act as dispersants in the dyeing process and also actas crystallization inhibitors in solution. The use of the carbonatecompounds of the present invention in place of conventional silicates orphosphorus prevents the discharge of untreatable toxic wastewater intonatural waterways.

The invention is also directed to buffered alkalis comprised of amixture of sodium and potassium hydroxides, and sodium and potassiumcarbonates, which exhibit the desired buffering while also exhibitingthe necessary active alkalinity to achieve dyeing with dyes such asvinyl sulfone dyes. The compositions may also include sodium citrate andpolyacrylic acid.

Accordingly, one aspect of the present invention is to provide a liquidcomposition for use in reactive dyeing of cotton and cotton blendedfabrics or the like. The composition includes an alkaline metalhydroxide, its carbonate and water and has a 2% pH value of greater thanabout 12 and a difference between the values of Total and ActiveAlkalinities of about 11.

Another aspect of the present invention is to provide a liquidcomposition for use in reactive dyeing of cotton and cotton blendedfabrics or the like. The composition includes: (a) up to about 12 wt %of an alkali metal hydroxide; (b) about 22 to 50 wt % of an alkali metalcarbonate; and (c) the balance water.

Another aspect of the present invention is to provide a liquidcomposition for use in reactive dyeing of cotton and cotton blendedfabrics or the like. The composition includes: (a) up to about 12 wt %of an alkali metal hydroxide; (b) about 22 to 50 wt % of an alkali metalcarbonate; (c) up to about 5 wt % of an alkali metal citrate; (d) up toabout 10 wt % of an alkali metal polyacrylate; and (e) the balancewater.

Still another aspect of the present invention is to provide a processfor preparing a liquid composition for use in reactive dyeing of cottonand cotton blended fabrics or the like. The process includes the stepsof: (a) introducing liquid caustic Potash into a reaction vessel; (b)adding caustic Potash flake to the mixture while mixing to adjust theamount of available alkali; (c) reacting the mixture with CO₂ whilemixing; (d) stopping the CO₂ when the value of a 2% pH solution is about12; and (e) cooling the mixture.

Yet another aspect of the present invention is to provide a liquidcomposition especially useful in the reactive dyeing of textilescomprised of (a) about 1 to about 50 wt % of sodium hydroxide; (b) up toabout 10 wt % of potassium hydroxide; (c) about 1 to about 50 wt % ofpotassium carbonate; (d) up to about 5 wt % of an alkali metal citrate;(e) up to about 10 wt % of an alkali metal polyacrylate; and (f) thebalance water.

Yet another aspect of the present invention is to provide a process forpreparing a liquid composition useful in the reactive dyeing of textilesincluding the steps of: (a) reacting potassium hydroxide with CO₂ toform an aqueous mixture of potassium hydroxide and potassium carbonate,and (b) adding sodium hydroxide to the mixture.

These and other aspects of the present invention will become apparent tothose skilled in the art after a reading of the following description ofthe preferred embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The Total and Active Alkalinities and 2% pH of the commerciallyavailable alkalis of sodium carbonate, Alkaflo, and Burco NP-Q solutionswere measured, as shown in Table 1, in order to determine screeningcriteria for other candidate materials. The sodium carbonate saturatedsolution had good Total and Active Alkalinity values but the 2% pH valuewas low, thereby requiring too much solution be added to the dye bath.The Alkaflo values were good but, as discussed above, this material ishigh in undesirable phosphorus. Finally, Burco NP-Q did not have a largeenough difference in its Total and Active Alkalinity values for goodbuffering.

Sodium carbonate and potassium carbonate were next added to Burco NP-Qto attempt to achieve the desired buffer effects. Potassium carbonatewas found to be the best additive, but a maximum of 12% carbonate wasall that could be post added without settling. As can be seen in Table1, the 12% carbonate was not enough to properly effect the dyeingproperties of the alkali since the 2% pH was only 11.3.

Various alternative approaches were considered to increase the level ofcarbonate in the liquid alkali, including adding stabilizing agents toprevent settling of the excess carbonate. However, these approaches wereunsuccessful. Finally, the present invention is based on the idea offorming the carbonate component of the mixture “in situ” by using thealkalinity of either NaOH or KOH to form potassium carbonate and sodiumcarbonate by reaction with either gaseous or liquid carbon dioxide(CO₂). It was surprisingly discovered that this process permitted theformation of a supersaturated carbonate solution, thereby providingsufficient carbonate to be available for dyeing without settlingproblems.

In the preferred embodiment, the process for preparing the liquid alkalicomposition of the present invention includes the steps of: introducingliquid caustic Potash into a reaction vessel; adding caustic Potashflake to the mixture while mixing to adjust the amount of availablealkali; reacting the mixture with CO₂ while mixing; stopping the CO₂when the value of a 2% pH solution is about 12; and cooling the mixture.An apparatus suitable for carrying out this reaction is disclosed inU.S. Pat. No. 5,059,407, issued to Wallace et al., the entire disclosureof which is hereby incorporated by reference.

In an alternative embodiment, the process also included adding up toabout 5 wt % citric acid and up to about 10 wt % polyacrylic acid to theliquid caustic Potash while mixing before the step of adding the causticPotash flake to the mixture. The citrate and polyacrylate act asdispersants in the dyeing process and also act as crystallizationinhibitors in solution. However, additional tests have shown that themixture can be made without the citrate or the polyacrylate and stillremain stable. Also, both processes preferably include filtering themixture through a one micron or smaller filter.

When the alkali composition is to be used in dyeing textiles withreactive dyes such an vinyl sulfone dyes, an increase in the activealkalinity of the composition is required. In such instances thepreferred compositions are prepared by the addition of sodium hydroxide,e.g., in the form liquid caustic (NAOH liq. 50%), to the aforesaidcompositions in an amount sufficient to increase the active alkalinityof the composition to the desired level while maintaining the desiredbuffering.

More specifically, between about 1 to about 50 parts by weight of sodiumhydroxide are added to between about 1 to about 50 parts by weight ofthe above buffered composition to increase the active alkalinity to thedesired level, resulting in an aqueous composition comprised of about 1to about 50 wt % of sodium hydroxide, up to about 10 wt % potassiumhydroxide, and about 1 to about 50 wt % potassium carbonate. Otheringredients such as alkali metal citrates and alkali metal polyacrylatesmay also be present.

The resultant composition, depending upon the specific end use desired,will have a pH of at least about 10, and preferably between about 10.5to about 12.5, an active alkalinity of between about 5 to about 38, anda total alkalinity of between about 10 to about 38. Normally, the ratioof total alkalinity to active alkalinity will be between about 1:1 toabout 2:1.

EXAMPLES 1-5

Each of the candidate materials was tested for both Total and ActiveAlkalinity. Active Alkalinity is the amount of alkali titratable withstrong acid to the phenolphthalein end-point. Total Alkalinity is theamount of alkali titratable with strong acid to the methyl orangeend-point. The results of the initial screening of the candidatesolutions is shown in Table 1, below:

TABLE 1 Total and Active Alkalinities of Selected Alkali Example AlkaliActive Alk Total Alk 2% pH 1 Sodium Carbonate 29 58 11.3 2 Alkaflo 12.516.7 12.3 3 Burco NP-Q 14.0 18.8 12.5 4 NPQ plus Carbonate 9.5 21.1 11.35 Present Invention 10.9 22.0 12.2

The above examples illustrate that only the present invention, having anexcess of carbonate, has a 2% pH value of greater than about 12 and adifference between the values of Total and Active Alkalinities of about11. The importance of these values will be shown more clearly understoodby a review of the following dyeing tests.

It was determined that the ideal pH for all types of reactive dyeing wasclosest to sodium carbonate pH=10.5-11.0. Since this pH range isindicative of that achievable with sodium carbonate, dyeings were madeat an equal shade depth using 20% sodium carbonate, 5, 10, 15, and 20%NPQ salt and 10 and 20% NPQ Carbonate as the alkali systems. The presentinvention was then prepared maximizing the potassium hydroxideconcentration and carbonating the material to achieve a higher thanequilibrium potassium carbonate yield while maintaining solubility.Dyeings were made and compared to the sodium carbonate and NPQ Salt. Theresults are shown below in Examples 6-27 in comparison with the otherdye trials.

EXAMPLES 6-27

Conventional reaction dyeings of cotton fabrics were made to determinethe dye yield of the candidate materials. The dyes selected wereProcion™ Red HE7B, Reactive Red 141, and Procion™ Red HE3B, Reactive Red120. These dyes are Monochlortriazine dyes and are available from ICIAmerica of Wilmington, Del. These dyes were chosen because the HE3B isextremely sensitive to high active alkalinity; it dyes weak when toomuch alkalinity is used because of hydrolysis. The HE7B was used becauseit dyes weak unless a high enough active alkalinity is used because oflow fixation of dye to fiber at lower active alkali values. Thus, thesedyes represent the extremes likely to be encountered.

TABLE 2 HE7B Dye Trial Results Example Alkali Conc. Suitable Weak orStrong 6 S. Carbonate 20% Y Standard 7 NPQ Salt  5% Y Standard 8 NPQSalt 10% Y Standard 9 NPQ Salt 15% Y Standard 10 NPQ Salt 20% Y Standard11 NPQ Carb 10% N Weak 12 NPQ Carb 20% Y Standard 13 Invention  5% NWeak 14 Invention 10% Y Standard 15 Invention 15% Y Standard 16Invention 20% Y Standard

TABLE 3 HE3B Dye Trial Results Example Alkali Conc. Suitable Weak orStrong 17 S. Carbonate 20% Y Standard 18 NPQ Salt  5% N Weak 19 NPQ Salt10% N Weak 20 NPQ Salt 15% N Weak 21 NPQ Salt 20% N Weak 22 NPQ Carb 10%N Weak 23 NPQ Carb 20% Y Standard 24 Invention  5% N Weak 25 Invention10% Y Standard 26 Invention 15% Y Standard 27 Invention 20% Y Standard

These results clearly show that the present invention will yield on thealkali sensitive HE3B at both equal concentrations to sodium carbonateand at lower concentrations to sodium carbonate since at less than 20%,sodium carbonate does not have enough alkalinity to cause the dye toreact with the fiber. The above examples also show that the presentinvention is an acceptable substitute for phosphorus-based alkali forreactive dyeing of cotton and cotton blended fabrics or the like.

The amount of carbonate in the present invention can be varied between alow of about 22 to a high of about 45 wt % with 40 wt % being mostpreferred. The amount of alkali metal hydroxide in the present inventionvaries between a low of about 4 to a high of about 12 wt % with 7 wt %being most preferred. Accordingly, the preferred composition has thefollowing properties:

Appearance: Clear liquid

Active Alk: 10.2-11.2

Total Alk: 20.5-22.0

2% pH: 12.2-12.4

Potassium Carbonate: 39.00-41.67 wt %

Potassium Hydroxide: 4.38-9.19 wt %

Potassium Citrate: 4 wt %

Potassium Polyacrylate 100000 mwt: 3.8 wt %

This provides a liquid alkali product that can be used at 10% on weightof fabric (OWF) in dyeing machines with liquor ratios from 1:1 up to100:1. At higher liquor ratios, a higher OWF may be necessary foracceptable yield.

EXAMPLES 28-30

A buffered alkali composition, referred to herein as SA-200, wasprepared by reacting potassium hydroxide with CO₂ while mixing until a2% pH solution was about 12. The SA-200 had an active alkalinity of 10.7and a total alkalinity of 21.7. The SA-200 was then mixed with sodiumhydroxide in the form of liquid caustic in different amounts until andthe active and total alkalinities of the resultant mixtures werecomparable to the alkalinities of Burco® NPQ salt and two commerciallyavailable alkalis used in the dyeing of textiles with vinyl sulfonedyes.

The following compositions were prepared. All amounts are in parts byweight:

TABLE 4 SA-200 and Liquid Caustic Example SA-200 Liquid Caustic SuitableWeak or Strong 28 19 29 Y Standard 29 40 24 Y Standard 30 10 26 YStandard

The carbonate content and the active and total alkalinities of thesecompositions were then compared to the commercially available products.

TABLE 5 Comparative Test Results Carbonate Active Total Burco ® NPQ Salt6.2 13.6 18 Example 28 5.3 13.64 15.5 Alkali A 13.4 14.4 22.2 Example 2912.2 14.28 18.39 Alkali B 0.0 11.8 12.3 Example 30 2.1 11.25 12.16

As can be seen, most possible combinations of active, total andcarbonate alkalinity can be made by mixing liquid caustic soda andSA-200.

Certain modifications and improvements will occur to those skilled inthe art upon reading of the foregoing description. By way of example,amino, polyphosphate, gluconate, and polymeric chelating agents arepossible substitutes for polyacrylic acid. Also, other additives mayinclude phosphoric acid derivatives and alkaline stable surfactants. Itshould be understood that all such modifications and improvements havebeen deleted herein for the sake of conciseness and readability but areproperly within the scope of the following claims.

I claim:
 1. A clear stable, supersaturated, phosphorous-free andsilicate-free, aqueous solution for reactive dyeing of cotton and cottonblended fabrics, said solution comprising: (a) about 1 to about 50 wt %of sodium hydroxide; (b) potassium hydroxide in an amount of about 4 toabout 10 wt %; and (c) about 1 to about 50 wt % of potassium carbonate,wherein said solution has a pH of at least 10, an active alkalinity ofbetween about 5 to about 38, and a total alkalinity of between about 10to about
 38. 2. The solution according to claim 1, further including upto about 5 wt % of an alkali metal citrate.
 3. The solution according toclaim 1, further including up to about 10 wt % of an alkali metalpolyacrylate.
 4. A clear, stable, supersaturated, phosphorous-free andsilicate-free aqueous solution for reactive dyeing of cotton and cottonblended fabrics, said solution comprising: (a) about 1 to about 50 wt %of sodium hydroxide; (b) potassium hydroxide in an amount of about 4 toabout 10 wt %; (c) about 1 to about 50 wt % of potassium carbonate; (d)up to about 5 wt % of an alkali metal citrate; (e) up to about 10 wt %of an alkali metal polycrylate; and (f) the balance water, wherein saidsolution has a pH of at least 10, an active alkalinity of between about5 to about 38, and a total alkalinity of between about 10 to about 38.